Three-dimensional printing is a process of making a three-dimensional solid object of virtually any shape from a digital model. One approach to three-dimensional printing uses an additive process in which one or more printheads eject successive layers of material on a substrate in different shapes. This approach to three-dimensional printing is also known as additive manufacturing. The substrate is supported on a platform that can be moved in one, two, or three dimensions by operation of actuators operatively connected to the platform. Additionally or alternatively, the printhead or printheads are also operatively connected to one or more actuators for controlled movement of the printhead or printheads to produce the layers that form the three-dimensional object. Three-dimensional printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling.
The three-dimensional additive process is performed in a printer in a layer-by-layer manner. To operate the ejectors in the printhead(s) to form a layer, a three-dimensional raster processor receives a file of three-dimensional data of the part to be produced. These three-dimensional part data can be contained in a computer-aided design (CAD) file, for example. The processor uses these data to generate a raster data file, which contains data that correspond to each layer that forms the part. A printhead driver receives the raster data file and generates pixelated data that are used to operate the ejectors in the printhead(s) for the ejection of building and support material onto a support platen to form the part layer by layer. The printhead driver and a printer controller generate signals to coordinate the movement of the platen and the printhead(s) with the operation of the ejectors in the printhead.
The movement of the platen and printhead(s) in previously known printers is monitored with encoders and the like to enable the printer controller to operate actuators that move the platen and printheads in the horizontal plane to enable accurate positioning of those components. These position sensors can produce inaccurate readings, which can affect production of the part. Errors can also occur in the vertical direction. Sources of error in the vertical are inaccurate movement of the printhead, the platen, or both in the vertical direction, imprecise placement of the drops ejected by the printhead(s), and variation in the mass of the drops ejected from different inkjets or from mass variations occurring in inkjets over time. One way to address errors in the vertical direction is a planerizer. A planerizer contacts a surface of an object to remove excess material in a layer. One adverse impact of a planerizer is the waste of the removed material and the inaccurate operation of the planerizer that sometimes occurs. Consequently, operation of a printer capable of avoiding or compensating for vertical building errors would be advantageous.